Japanese Patent Application Publication No. 2005-515408 describes a cell treatment method when a flow cytometer or the like is applied for detection by the fluorescence in situ hybridization method (FISH method). According to the FISH method, cells are stained by pretreatment in which a labeled probe is hybridized with a DNA sequence region to be detected in a cell, and the fluorescence generated due to the labeled probe is detected so as to detect the abnormal cells.